The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head with a flexible membrane for chemical mechanical polishing.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly nonplanar. This nonplanar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a xe2x80x9cstandardxe2x80x9d or a fixed-abrasive pad. A standard polishing pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. Some carrier heads include a flexible membrane that provides a mounting surface for the substrate, and a retaining ring to hold the substrate beneath the mounting surface. Pressurization or evacuation of a chamber behind the flexible membrane controls the load on the substrate. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad.
The effectiveness of a CMP process may be measured by its polishing rate, and by the resulting finish (absence of small-scale roughness) and flatness (absence of large-scale topography) of the substrate surface. The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad.
A reoccurring problem in CMP is the so-called xe2x80x9cedge-effect,xe2x80x9d i.e., the tendency of the substrate edge to be polished at a different rate than the substrate center. The edge effect typically results in overpolishing (the removal of too much material from the substrate) at the substrate perimeter, e.g., the outermost five to ten millimeters of a 200 millimeter (mm) wafer.
In one aspect, the invention is directed to a carrier head for chemical mechanical polishing. The carrier head has a base, a flexible membrane extending beneath the base to define a pressurizable chamber, an edge load ring and a retaining ring. A lower surface of the flexible membrane provides a substrate receiving surface of a substrate and includes a first surface to apply a first pressure to a first portion of the substrate. A second surface surrounds the first surface to apply a second pressure on a second portion of the substrate, and the edge load ring surrounds the second surface. A lower surface of the edge load ring provides a third surface to apply a third pressure to a third portion of the substrate surrounding the second portion. The retaining ring surrounds the edge load ring to maintain the substrate beneath the first, second and third surfaces.
Implementations of the invention may include one or more of the following features. An annular wall portion may surround and connect to the first surface of the flexible membrane. The wall portion may have a lower surface and an upper surface, the lower surface defining the second surface. A spacer ring may have a lower surface and an upper surface. The upper surface of the spacer ring may be arranged to receive a load in response to the pressurization of the chamber, and the lower surface of the spacer ring may abutting the upper surface of the wall portion, whereby the load received on the upper surface of the spacer ring is transferred to the wall portion. The spacer ring may be positioned between the edge load ring and the wall portion, or on the wall portion and substantially horizontally aligned with a top portion of the edge load ring. A surface area of the upper surface of the spacer ring may be greater than or substantially the same as a surface area of the lower surface of the spacer ring. The edge load ring may includes a top portion extending over the upper surface of the wall member and defining an upper surface of the edge load ring, and the upper surface may be configured to receive a load in response to the pressurization of the chamber and apply the second pressure to the second portion of the substrate and the third pressure to the third portion of the substrate. A surface area of the top surface of edge load ring may be greater than or less than a surface area of the lower surface of the edge load ring.
In another aspect, the invention is directed to a carrier head for chemical mechanical polishing. The carrier head has a base, a base, a flexible membrane extending beneath the base to define a pressurizable chamber, an edge load ring, and a retaining ring. A lower surface of the flexible membrane provides a first surface to apply a first pressure to a first portion of a substrate. The edge load ring surrounds the first surface and has an upper surface and a lower surface. The lower surface of the edge load ring provides a second surface for applying a second pressure to a second portion of the substrate. A surface area of the upper surface of the edge load ring is at least fifty percent of a surface area of the lower surface of the edge load ring. The retaining ring surrounds the edge load ring to maintain the substrate beneath the first and second surfaces.
Implementations of the invention may include one or more of the following features. The flexible membrane may include an annular wall portion providing a third surface to apply a third pressure to a third portion located between the first portion and the second portion of the substrate. A spacer ring may be positioned above an upper surface of the wall portion and may cooperate with the edge load ring to provide the third pressure to the third portion of the substrate.
In another aspect, the invention is directed to a carrier head for chemical mechanical polishing. The carrier head has a base, a flexible membrane extending beneath the base to define a pressurizable chamber, an edge load ring and a retaining ring. A lower surface of the flexible membrane provides a substrate receiving surface for a substrate. The lower surface includes a first surface to apply a first pressure to a first portion of the substrate and a second surface to apply a second pressure to a second portion surrounding the first portion. The edge load ring surrounds the second surface, and a contact surface of the edge load ring provides a third surface for applying a third load to a third portion of the substrate surrounding the second portion. The retaining ring surrounds the edge load ring to maintain the substrate beneath the first, second and third surfaces.
In another aspect, the invention is directed to a method of polishing a substrate. In the method, a substrate is brought into contact with a polishing surface, a first pressure to a first portion of the substrate with a first portion of a flexible membrane, a second pressure is applied to a second portion of the substrate with a second portion of the flexible membrane, and a third pressure is applied to a third portion of the substrate with an edge load ring.
Possible advantages of implementations of the invention may include one or more of the following. Overpolishing and underpolishing at the perimeter of a substrate can be reduced by applying different pressures on selected regions of the substrate.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other advantages and features of the invention will be apparent from the following description, including the drawings and claims.